Observations and impacts of transported Canadian wildfire smoke on ozone and aerosol air quality in the Maryland region on June 9–12, 2015

Abstract

Canadian wildfire smoke impacted air quality across the northern Mid-Atlantic (MA) of the United States during June 9-12, 2015. A multiday exceedance of the new 2015 70-ppb National Ambient Air Quality Standard (NAAQS) for ozone (O 3 ) followed, resulting in Maryland being incompliant with the Environmental Protection Agency's (EPA) revised 2015 O 3 NAAQS. Surface in situ, balloon-borne, and remote sensing observations monitored the impact of the wildfire smoke at Maryland air quality monitoring sites. At peak smoke concentrations in Maryland, wildfire-attributable volatile organic compounds (VOCs) more than doubled, while non-NOx oxides of nitrogen (NOz) tripled, suggesting long range transport of NOx within the smoke plume. Peak daily average PM 2.5 was 32.5 µg m −3 with large fractions coming from black carbon (BC) and organic carbon (OC), with a synonymous increase in carbon monoxide (CO) concentrations. Measurements indicate that smoke tracers at the surface were spatially and temporally correlated with maximum 8-hr O 3 concentrations in the MA, all which peaked on June 11. Despite initial smoke arrival late on June 9, 2015, O 3 production was inhibited due to ultraviolet (UV) light attenuation, lower temperatures, and nonoptimal surface layer composition. Comparison of Community Multiscale Air Quality (CMAQ) model surface O 3 forecasts to observations suggests 14 ppb additional O 3 due to smoke influences in northern Maryland. Despite polluted conditions, observations of a nocturnal low-level jet (NLLJ) and Chesapeake Bay Breeze (BB) were associated with decreases in O 3 in this case. While infrequent in the MA, wildfire smoke may be an increasing fractional contribution to high-O 3 days, particularly in light of increased wildfire frequency in a changing climate, lower regional emissions, and tighter air quality standards.Implications: The presented event demonstrates how a single wildfire event associated with an ozone exceedance of the NAAQS can prevent the Baltimore region from complying with lower ozone standards. This relatively new problem in Maryland is due to regional reductions in NOx emissions that led to record low numbers of ozone NAAQS violations in the last 3 years. This case demonstrates the need for adequate means to quantify and justify ozone impacts from wildfires, which can only be done through the use of observationally based models. The data presented may also improve future air quality forecast models.PAPER HISTORY

Joint measurements of PM<sub>2. 5</sub> and light-absorptive PM in woodsmoke-dominated ambient and plume environments

“…DC is strongly linked to the season, with highest values in the winter months and much lower values during the summer months. The summertime DC was close to zero, and the non-zero values could be attributed to Canadian forest fire events typically taking place during summer months (Dreessen et al, 2016;Dutkiewicz et al, 2011) and other recreational biomass burn- ing activities. DC, BC (880 nm) and PM 2.5 all peaked in winter months, when they showed very similar temporal trends.…”

Wildfire smoke exposure and human health: Significant gaps in research for a growing public health issue

“…The presence of these precursor species mean that smoke from wildfires can contribute to local spikes in ozone far from the source, just as the oxidative species in fine particulate matter can travel far downwind of the source. This was the case in Maryland in 2015, when smoke from a large wildfire in Canada caused Maryland to exceed National Ambient Air Quality Standards (NAAQS) (Dreessen et al, 2016). Therefore, populations downwind of a wildfire may be at great risk of exposure to oxidative chemical species (Urbanski et al, 2008).…”

Quantifying the contribution of thermally driven recirculation to a high-ozone event along the Colorado Front Range using lidar

“…The mixing heights at FTCW, defined by the largest O 3 gradient, are at 2.7 km above sea level (asl), 2.9 km asl, and 3.3 km asl, respectively, at 2010 UTC, 2130 UTC, and 2220 UTC. The TROPOZ measurements, which have previously used O 3 gradients to determine mixing heights [ Dreessen et al ., ], show a well‐defined O 3 gradient between defining the top of the mixed layer from 2.5–3.4 km asl throughout the day, which compares well with the aircraft and sonde. The TROPOZ observations indicate that the O 3 mixing height continued to grow throughout the day, even as solar radiation began to diminish, indicating that O 3 mixing likely persisted throughout the evening hours.…”